The presently disclosed embodiments relate generally to layers that are useful in imaging apparatus members and components, for use in electrostatographic, including digital, apparatuses. More particularly, the embodiments pertain to robust undercoat layer comprising TiSi in which the TiO2 to SiO2 ratio falls in a particular ratio range discovered to reduce both plywood print defects as well as undesirable electrical performance and print defects from micro-cracks in the undercoat layer, and methods for making the same.
Electrophotographic imaging members, e.g., photoreceptors, photoconductors, imaging members, and the like, can include a photoconductive layer formed on an electrically conductive substrate. The photoconductive layer is an insulator in the substantial absence of light so that electric charges are retained on its surface. Upon exposure to light, charge is generated by the photoactive pigment, and under applied field charge moves through the photoreceptor and the charge is dissipated.
In electrophotography, also known as xerography, electrophotographic imaging or electrostatographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. Charge generated by the photoactive pigment move under the force of the applied field. The movement of the charge through the photoreceptor selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image. This electrostatic latent image may then be developed to form a visible image by depositing oppositely charged particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
An electrophotographic imaging member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. In addition, the imaging member may be layered. These layers can be in any order, and sometimes can be combined in a single or mixed layer.
Multilayered photoreceptors or imaging members can have at least two layers, and may include a substrate, a conductive layer, an optional charge blocking layer (sometimes referred to as an “undercoat layer”), an optional adhesive layer, a photogenerating layer (sometimes referred to as a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, an optional overcoating layer and, in some belt embodiments, an anticurl backing layer. In the multilayer configuration, the active layers of the photoreceptor are the charge generation layer (CGL) and the charge transport layer (CTL). Enhancement of charge transport across these layers provides better photoreceptor performance. Overcoat layers are commonly included to increase mechanical wear and scratch resistance. In conventional photoreceptors, mechanical wear due to cleaning blade contact or scratches due to contact with paper or carrier beads causes photoreceptor devices to fail. As such, overcoat layers are employed to extend the life of the photoreceptor.
Current manufacturing processes of photoreceptor undercoat layers having TiSi formulation results in inconsistent product performance. For example, some photoreceptors can exhibit high Vlow, high Vresidual, reduced photosensitivity, and print defects. As used herein, Vlow refers to the surface voltages of photoreceptor after light exposure, Vresidual refers to the surface voltages of photoreceptor after erase light exposure, and “photosensitivity” refers to the surface voltage change rate to the exposure energy. It was observed that the abnormal electrical performance and defects are related to micro-cracks within the TiSi under coat layer. In addition, TiSi undercoat layers can also suffer from “plywood effect,” a print quality defect.
Coherent illumination is used in electrophotographic printing for image formation on photoreceptors. Unfortunately, the use of coherent illumination sources in conjunction with multilayered photoreceptors results in the “plywood effect,” also known as “interference fringe effect.” This defect consists of a series of dark and light interference patterns that occur when the coherent light is reflected from the interfaces that pervade multilayered photoreceptors. In organic photoreceptors, primarily the reflection from the undercoat layer or charge blocking layer/substrate interface (e.g., substrate surface) or the reflected light from the undercoat layer (or charge blocking layer)/charge generating layer interface account for the interference fringe effect. The effect can be eliminated if the strong undercoat layer surface reflection or the strong substrate surface reflection is eliminated or suppressed.
Thus, there is a need for an improved imaging layer that does not suffer from the above-described problems.
Conventional photoreceptors are disclosed in the following patents, a number of which describe the presence of light scattering particles in the undercoat layers: Yu, U.S. Pat. No. 5,660,961; Yu, U.S. Pat. No. 5,215,839; and Katayama et al., U.S. Pat. No. 5,958,638. The term “photoreceptor” or “photoconductor” is generally used interchangeably with the terms “imaging member.” The term “electrostatographic” includes “electrophotographic” and “xerographic.” The terms “charge transport molecule” are generally used interchangeably with the terms “hole transport molecule.”